2011 Conversion Rates

Is anyone else seeing extremely low conversion rates of glu/fru to etoh for the 2011 vintage? On the lots I’ve tested so far, I’m getting 0.565 to 0.575, whereas the last 15 years or so it’s been between 0.59 to 0.6.

Not sure if this has been discussed already in Cellar Rats, if so, let me know.

Ed: I stopped doing all the calculations and post-crush rechecking for red must, I guess because I finally came to terms with the fact that it was all a WAG anyways. But, yes, I would say that for both 2010 and 2011, the conversions were lower than I would have instinctively thought them to be. I used to use glu+fru % x 0.59 and it worked out pretty well. Still does for whites for me, but with all the convoluted factors for red must, 2010 left me scratching my head and I didn’t even bother measuring glu/fru in '11 and just used Brix instead.

My guess is less tiny berry raisins in the clusters due to colder weather - so less soak up of extra sugar once fermentation starts. I always thought higher conversion rates were the result of not being able to truely measure accurate sugar levels, especially with riper fruit - or basically a form of “human error”, or maybe more correctly a limitation of the measurements.

I think that is why it is so hard top get good numbers on Zin sometimes. There are times when it is still soaking up when the fermentation starts, so you never truly know what the Brix are.

Zin is definitely tougher to measure accurately. And how about whole-cluster fermentations…I’ve had a harder time getting good numbers on the few ones I’ve worked with. Any tips on those?

I fully agree about the mysterious Zin soak ups. In 2010 my Zin was picked at 21.8 brix and right before fermentation really kicked in, it was 25 in the tank, but probably kept going up.

Whole cluster brix readings are very tough to get, I try to take as random a sample as possible, kind of like vineyard sampling, but in a tank.

I also agree that it’s tough to get solid brix readings pre fermentation, and maybe there was just less soak up in 2011. Good point, Uncle Brian!

Do you jump into tank with your scuba gear on? [wow.gif]

Glad you posted this Ed- I was thinking there was some strange shit goin’ down at my place.

My standard practice is to cold soak for 7 days- and get glu/fru and around day 6 to get a real grasp on where things are. I run alc too just to be sure there weren’t some cold-friendly strains gettin’ busy andthrowin’ off my calcs.

Last year we had a range of conversions from .56 to .61- with more in the lower range than higher. This year all except one were .55/.56 which really perplexes me- except the last one came in at .62, which perplexes me even more.

All unninoculated, and no DAP, Fermaid, etc etc of any kind (plus no animals were harmed in the making of these wines- excpet the interns, but they don’t really count).

Someday, I may understand what the hell I am doing, but that day is still several lifetimes away.

Ed:

.58 to .60 here… and same here that I can never seem to get an accurate sample from the whole cluster lots. They always start with the lowest glu/fru but finish with slightly higher alcohols.

I was in the .55 - .56 range this year

.55 on whole cluster Santa Barbara Highlands Mourvèdre
.55 on whole cluster Shake Ridge Mourvèdre (looking at the numbers on this one doesn’t make any sense)
.55 - .56 on our Yountville Semillon (1/2 on skins, 1/2 in egg)

In general, conversions in the cellar were seemingly low across the board with reds lower than the whites.

I saw 0.6 conversion on Chenin Blanc from Clarksburg this year, but .55 and .56 almost across the board on Napa Cabernet…with no apparent rate differentiation between native and manufactured yeasts. Even harder for me to pin down this year was the wide variation between vineyard sampling numbers and the numbers in tank…I was seeing uncommonly huge disparities there on certain lots, and I’m generally pretty meticulous with my vineyard sampling.

Is there really anything in winemaking that’s not a WAG? [scratch.gif]

Newbie question: Are you all finding your conversion rates by working the equation backwards? Also, is there a common consensus on using glucose + fructose % versus using brix and a pre-determined conversion rate?

Different shades of gray, I suppose. This topic seems to lead to the most head-scratching for me, though.

Yeah to the first question. To the second, if you really care about finished alcohol (I have become less and less concerned other than if it is obscenely low or high), glu + fru would be the way I would proceed, personally. Brix (or Baume or the myriad other must density measurements) is a way to take something that is somewhat difficult to measure, fermentable sugar, and approximate it in a way that is simple to measure. I’ve found that when you have a precise measurement, in a tank of white juice for example, using %glu + fru x your conversion rate (I’ve always used 0.59) leads to few surprises. Unfortunately, for all the reasons in this thread, it is much more difficult with red must. Amount of whole berry, amount of whole cluster, raisins, green berries, length of soakup (and possible start of some fermentation during), quality of mixing, press cuts and so on all affect the finished outcome.

I’m sure I’m not the only one who has cursed when a tank seems to be stuck or sluggish at -0.8 Brix only to find via analysis that it’s dry…or been surprised when one chugging along at -1.5 Brix still has 10g/L RS. It’s an imperfect measurement, but it’s easy and provides trends.

So, I’ve stopped measuring glu + fru in red must. If Brix suggests that a must might need some adjustment, I wait until about 8-12 Brix and then analyze RS and alcohol and use my conversions to see where that is heading before I do anything.

Nate is a genius.

Agreed on the genius.

Great responses, everyone!

Now with these lower alcohols and the warmer winter, I would’ve thought MLs would have been finished long ago. Not the case here in SF.

same here.

They’re going slow in Berkeley too.

+1

Gentlemen… heat your barrel rooms [cheers.gif] Our MLs finished a month ago [drinkers.gif]